If you are traveling overseas and don’t want to pay a ton of money for your cell calls, this column is for you.

This week, I am in Australia speaking at a security conference and I thought I would share with you both my research and the actual results.

The issue is that international roaming is expensive with your US-based cell phone. If you want to keep in touch with family and business colleagues back home when you travel, you have the following alternatives

Buy a phone calling card once you get to your destination and use it from payphones or your hotel,

Don’t do anything and use your existing US phone,

Use Skype (or something similar) and your computer to make VOIP calls

Buy a new SIM module for your existing phone, or

Buy a new SIM module and a new phone.

The calling card is a decent option, depending on where you are going and what your hotel charges for both toll-free and local calls. Some are still back in the profiteering stone ages and charge almost as much as the cell providers on a per-minute basis, even to make a local call or to connect to the calling card provider. You should know that some calling cards may not work with some pay phones, according to Dan Dern. He also reminds me that you might want to invest in a DMTF tone generator if you need to call back to a stateside answering machine – some foreign phones don’t generate the correct touch tones. You can use the Java applet on your computer here.

Skype is another option, and there are various plans and you can assign local in-country numbers to the same account. You do need a computer and a headset to make calls, though, which may not work for everyone.

The other options will only work if you have at least a tri-band phone on either T-Mobile or AT&T/Cingular networks. If you are using Verizon or Sprint, you need a new phone. Most of the world’s cell phones (except in Japan and a few other places), work on what is called the GSM networks that operate at either 900 MHz or 1800 MHz. The US and Canada GSM networks operate at 850 MHz and 1900 MHz. So if you have a phone that can work on at least three of the four bands, you should be set to roam abroad. You should check the service of your country, though, because some of them have the older GSM 900 networks and some of the tri-band phones only offer 1800 MHz service.

So we arrive at the last options, and here is where things get interesting. Before I get any further, let me explain that your cell phone has two important pieces: one is the phone itself, and this makes a difference with the number of radio bands that it works on. But the second piece is the SIM card that is inside the phone, and if you are like most normal people you probably haven’t given this little thing much thought – until now. This SIM card is what is used by the phone to store your address book and also gives your phone your inbound number and identity on the cell network. It is about the size of a microSD memory card.

If you replace the SIM card that came with your phone with a card that works in the country you are visiting, you get several benefits. First, you don’t pay roaming charges for local in-country calls, although if you are calling back to the States, you will pay international long distance charges. Second, if people in-country are trying to reach you, they don’t pay for the international calls either. (Some of the networks overseas have the more enlightened method of calling party pays, but we won’t go there for now.) You also don’t use any minutes on your American cell accounts, which can be good if you have a limited number of minutes – when you travel, you don’t think about all the time you are on calls. The trouble is if you are going to several different countries, then you need different SIMs and have to keep track of the numbers too. That gets onerous.

So there is another solution: buy a SIM card from one of two suppliers that have interesting programs for travelers. The two are called telestial.com and Maxroam.com. They both offer a SIM card that will work around the globe, and have reasonable per-minute calling rates. Both make use of dial-back services, so when you place your cell call you actually setting up an IP conference call that the provider originates – that is how they give you the price break. With both services, you don’t have to sign a contract, the SIMs are reasonable, and you can add more minutes to your account easily over the Web and charge your credit card.

Maxroam has the better Web tools -- you can set up your number to automatically forward to a series of numbers, so that you can be more easily reached as you travel., You pick a US-based number for your phone, and pay a small monthly fee for each number in the countries that you are visiting. They have a wide selection.

Telestial gives you one number (mine was based in the UK) and then a series of toll-free numbers in the various countries that you travel. For your correspondents to reach you in these countries, they can either dial the UK number directly, or dial the toll free number and then key in your number – that is a lot of digits to dial. Your callers don’t pay for their calls, but you do and it is a big bite about $1.50 a minute from the US to Australia. The plus side is that incoming calls to your phone don’t consume any minutes, if they dial your number directly.

There is just one catch. Chances are, your cell phone is locked to your carrier that you are currently using. This means if you try to take out your SIM card and replace it with one of these new cards, your phone won’t work. You might be able to receive calls, but not make outgoing calls.

So how do you get your phone unlocked? You can pay for a special code that you enter and here is where things get dicey. Until recently, American cellular carriers claimed that unlocking was illegal. The laws are changing, but still many of the companies that provide this service have the feeling of going to the seedy side of town where goods are bought in cash through an open car window, not that I conduct my business in this fashion, you should know.

There are a number of unlocking providers, here are just a few and what they charge per phone to unlock:

Uniquephones.com $15

Gsmliberty.com $25

Cellularunlockcodes.com $20

Unlockexperts.co.uk $13

Cellularlocksmith.com $20

Cellphonerepair.org $25

All of them work by first charging your credit card the fee, and then sending you the code via email. Sometimes they take their sweet time in sending this code.

I got two phones unlocked for my trip: for one, I used Uniquephones and somehow they “lost” my order, and only when I emailed their executives and spoke to them personally (they are based in the UK), did I get my code delivered. I also called AT&T directly, and it took several calls with what they call their customer service line before they gave me the code, and only after saying that I was about to leave the country and wasn’t going to wait for an answer. Obviously, this is still a difficult area and one that might give you some pause if you want this all to work before you step on a plane.

There are other services that have downloadable unlocking software, but that seems even more trouble. Once I got my code, it took seconds to enter it on my phone, and it was running on T-Mobile’s network with my new number from the Maxroam or Telestial folks. Sweet. (Do write down this code and take it with you on your trip, just in case you need to enter it again.)

What bothered me most about both services was that there is a delay while the conference call is being set up. Those of us that are used to instantly calling someone will have to wait a few seconds before your cell phone rings back indicating the call is going through. And sometimes the voice quality was poor, or there were delays like talking to someone on the moon.

You have another option, and that is to still buy one the SIM cards but get a new phone that comes unlocked. If you are a Verizon or Sprint user, this is really your only option. There are many Web sites that offer to sell you unlocked models. The least expensive phones that I could find (that were at least a tri-band GSM model) were on TigerDirect.com – they were selling a Motorola V180 for $50. And Amazon.com has a Motorola V220 for $70. Neither of these phones is going to win any design awards, but they will do the job.

Plan on taking a few weeks to negotiate all of these options, so don’t do this a few days before you have to leave the country. And you might want to bring along your current SIM card, just in case.

Good luck with your travels, and do let me know if you have better solutions that have worked for you.